This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/JP00/02400 which has an International filing date of Apr. 13, 1999, which designated the United States of America.
The present invention relates to a rubber composition. More particularly, it relates to a rubber composition having excellent appearance, fluidity, abrasion resistance and mechanical strength.
There have already been known thermoplastic elastomer compositions obtained by so-called dynamic crosslinking, namely, crosslinking a radical crosslinkable elastomer and a resin having no radical crosslinkability, such as polypropylene, under melt-kneading them in an extruder in the presence of a radical initiator, and these compositions are widely employed for uses such as automobile parts.
There have been known techniques which use ethylene-propylene-diene rubbers (EPDM) or olefin elastomers produced with metallocene catalysts (JP-A-9-104787) as the said elastomer compositions. However, such compositions are not necessarily sufficient in mechanical strength, and by increasing the amount of elastomer component, mechanical strength can be improved, but appearance and fluidity are considerably deteriorated. Under the circumstances, it is demanded to provide practically acceptable rubber compositions excellent in appearance, fluidity and mechanical strength.
On the other hand, thermoplastic compositions obtained by crosslinking metallocenic olefin rubbers are disclosed (JP-A-9-137001, JP-A-10-287775). However, these patent publications do not mention post-addition of a thermoplastic elastomer to the crosslinked product.
Furthermore, there are disclosed a composition obtained by crosslinking an oil-extended olefin copolymer rubber, an olefin resin and a softening agent with an organic peroxide and then adding to the crosslinked product a hydrogenated styrene thermoplastic elastomer (JP-A-3-292342), a composition obtained by subjecting to partial crosslinking an olefin rubber, an olefin resin, a softening agent and a filler with an organic peroxide and adding an A-(B-A)n type block copolymer to the crosslinked product (JP-B-3-58381), and a composition comprising a crosslinked rubber-containing thermoplastic elastomer, a styrene-based block copolymer, a softening agent and a polyolefin resin (JP-A-7-11067). The compositions disclosed in the above patent publications are improved in tackiness and bleeding properties by the post-addition of the thermoplastic elastomer, but are inferior in appearance, fluidity, abrasion resistance and mechanical strength and practically unusable because of using no specific metallocenic ethylene-xcex1-olefin copolymer. Moreover, the above patent publications neither mention nor suggest that the abrasion resistance is remarkably improved by the post-addition of a thermoplastic elastomer to a thermoplastic crosslinked product of a metallocenic ethylene-xcex1-olefin copolymer. Under the circumstances, demanded is a practically usable rubber composition excellent in appearance, fluidity, abrasion resistance and mechanical resistance.
In view of the problems mentioned above, the object of the present invention is to provide a rubber composition having excellent appearance, fluidity, abrasion resistance and mechanical strength.
As a result of intensive research conducted by the inventors in an attempt to solve the above problems, it has been surprisingly found that appearance, fluidity, abrasion resistance and mechanical strength are markedly improved when a thermoplastic elastomer is added later to a partially or completely crosslinked product having a specific crosslinked structure and containing a specific ethylene-xcex1-olefin copolymer and an olefin resin, and, as a result, the above problems have been solved. Thus, the present invention has been accomplished.
That is, the present invention is a rubber composition which contains a thermoplastic partially or completely crosslinked product comprising 1-99 parts by weight of an ethylene-xcex1-olefin copolymer (A) containing an ethylene unit and an xcex1-olefin unit of 3-20 carbon atoms and prepared using a metallocene catalyst and 1-99 parts by weight of an olefin resin (B) (the total amount of (A) and (B) being 100 parts by weight), the crosslinking degree of the ethylene-xcex1-olefin copolymer (A) being 50% or higher, and 1-500 parts by weight of a thermoplastic elastomer (C) added later to the crosslinked product.